The present invention relates to a document reading apparatus for reading a document and for outputting an image signal, especially having a function of determining an effective document region based on a detected data.
Conventionally, an apparatus capable of imaging an original document such as a book which is placed face up on a document holder is known. In an apparatus of this type, usually an operator has to set an imaging region of an original document. In a reading apparatus of the type wherein an original document is set face down on a document holder made of glass so as to be read from below, it is possible to arrange reflection type photo sensors below the glass document holder for detecting automatically size of the document. However, such a construction is hard to be applied to the type wherein the document is set face up to be read from above.
In an apparatus of this type, an operator must pay much attention at the time of imaging operation so that his hands or fingers pressing the document might not enter into the imaging region, since the hands or fingers is occasionally imaged together with the original document, causing the failure of imaging operation.